Introduce FrameOrImportedDocument

FrameFetchContext works for a frame and an imported document.
I'm planning to split more classes from FrameFetchContext
which will need the same logic.

This CL introduces FrameOrImportedDocument for the shared logic to avoid
future code duplication.

Bug: 914739
Change-Id: I75d59e5e53ae99cd945ed5e160142681d7f5f5c0
Reviewed-on: https://chromium-review.googlesource.com/c/1404902
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Hiroshige Hayashizaki <hiroshige@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621956}
5 files changed